In a Wireless Local Area Network (WLAN) comprising a number of access points (APs), mobile stations (STAs) roam from one AP to another as they change locations with their users. There are two ways for a mobile station to discover available access points to roam to. Either it can search periodically for alternatives, so that it has a list ready when it is ready to roam, or it can wait until it is necessary to roam to search for other access points. In the first approach, called pre-emptive discovery, a station periodically scans the WLAN channels to learn about its neighboring access points, in a process usually referred to as background scanning. This process may be either active, where the station sends probes out on all its channels to detect neighboring access points, or passive, where the station listens on all its channels for access point beacons. The frequency of background scans directly impacts the roaming performance of a WLAN device. If background scans are not performed frequently enough, the device may fail to pick the optimal access point while roaming, or even fail to find a neighbor and disconnect.
Decreasing the background scanning interval improves network connectivity performance; however, it also degrades battery life, because scanning is a process that consumes a significant amount of power. In selecting a scanning interval, a compromise is made between preserving battery power, and providing adequate roaming capabilities.
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